Platinum-ruthenium-palladium alloys for use as a fuel cell catalyst

ABSTRACT

A noble metal alloy composition for a fuel cell catalyst, a ternary alloy composition containing platinum, ruthenium and palladium. The alloy shows increased activity as compared to well-known catalysts.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/121,970, filed Feb. 26, 1999.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This was made with Government support under grant numberDE-FG03-97ER82492 awarded by the Department of Energy. The Governmenthas certain rights in this invention.

BACKGROUND OF THE INVENTION

1. Field of The Invention

The present invention relates to noble metal alloy catalysts, especiallyto platinum, palladium and ruthenium alloy catalysts, which are usefulin fuel cell electrodes and other catalytic structures.

2. Background Information

A fuel cell is an electrochemical device for directly converting thechemical energy generated from an oxidation-reduction reaction of a fuelsuch as hydrogen or hydrocarbon-based fuels and an oxidizer such asoxygen gas (in air) supplied thereto into a low-voltage direct current.Thus, fuel cells chemically combine the molecules of a fuel and anoxidizer without burning, dispensing with the inefficiencies andpollution of traditional combustion.

A fuel cell is generally comprised of a fuel electrode (anode), anoxidizer electrode (cathode), an electrolyte interposed between theelectrodes (alkaline or acidic), and means for separately supplying astream of fuel and a stream of oxidizer to the anode and the cathode,respectively. In operation, fuel supplied to the anode is oxidizedreleasing electrons which are conducted via an external circuit to thecathode. At the cathode the supplied electrons are consumed when theoxidizer is reduced. The current flowing through the external circuitcan be made to do useful work.

There are several types of fuel cells, including: phosphoric acid,molten carbonate, solid oxide, potassium hydroxide, and proton exchangemembrane. A phosphoric acid fuel cell operates at about 160-220° C., andpreferably at about 190-200° C. This type of fuel cell is currentlybeing used for multi-megawatt utility power generation and forco-generation systems (i.e., combined heat and power generation) in the50 to several hundred kilowatts range.

In contrast, proton exchange membrane fuel cells use a solidproton-conducting polymer membrane as the electrolyte. Typically, thepolymer membrane must be maintained in a hydrated form during operationin order to prevent loss of ionic conduction which limits the operationtemperature typically to about 70-120° C. depending on the operatingpressure, and preferably below about 100° C. Proton exchange membranefuel cells have a much higher power density than liquid electrolyte fuelcells (e.g., phosphoric acid), and can vary output quickly to meetshifts in power demand. Thus, they are suited for applications such asin automobiles and small scale residential power generation where quickstartup is required.

Conventional fuel cells use hydrogen gas as the fuel. Pure hydrogen gas,however, is difficult and costly to supply. Thus, hydrogen gas istypically supplied to a fuel cell using a reformer, which steam-reformsmethanol and water at 200-300° C. to a hydrogen-rich fuel gas containingcarbon dioxide. Theoretically, the reformate gas consists of 75 vol %hydrogen and 25 vol % carbon dioxide. In practice, however, this gasalso contains nitrogen, oxygen and, depending on the degree of purity,varying amounts of carbon monoxide (up to 1 vol %). This process is alsocomplex, adds cost and has the potential for producing undesirablepollutants. The conversion of a liquid fuel directly into electricitywould be desirable, as then a high storage density, system simplicityand retention of existing fueling infrastructure could be combined. Inparticular, methanol is an especially desirable fuel because it has ahigh energy density, a low cost and is produced from renewableresources. Thus, a relatively new type of fuel cell has been the subjectof a great amount of interest—the direct methanol fuel cell. In a directmethanol fuel cell, the overall process that occurs is that methanol andoxygen react to form water and carbon dioxide and electricity, i.e.,methanol combustion.

For the oxidation and reduction reactions in a fuel cell to proceed atuseful rates, especially at operating temperatures below about 300°C.,electrocatalyst materials are required at the electrodes. Initially,fuel cells used electrocatalysts made of a single metal, usuallyplatinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), osmium (Os),silver (Ag) or gold (Au) because they are able to withstand thecorrosive environment—platinum being the most efficient and stablesingle-metal catalyst for fuel cells operating below about 300° C. Whilethese elements were first used in solid form, later techniques weredeveloped to disperse these metals over the surface of electricallyconductive supports (e.g., carbon black) to increase the surface area ofthe catalyst which in turn increased the number of reactive sitesleading to improved efficiency of the cell. Nevertheless, fuel cellperformance typically declines over time because the presence ofelectrolyte, high temperatures and molecular oxygen dissolve thecatalyst and/or sinter the dispersed catalyst by surface migration ordissolution/re-precipitation (see, e.g., U.S. Pat. No. 5,316,990).

Although platinum is a good catalyst, concentrations of carbon monoxide(CO) above about 10 ppm in the fuel can rapidly poison the catalystsurface. As a result, platinum is a poor catalyst if the fuel streamcontains carbon monoxide (e.g., reformed-hydrogen gas typically exceeds100 ppm). Liquid hydrocarbon-based fuels (e.g., methanol) present aneven greater poisoning problem. Specifically, the surface of theplatinum becomes blocked with the adsorbed intermediate, carbon monoxide(CO). It has been reported that H₂O plays a key role in the removal ofsuch poisoning species in accordance with the following reactions:

Pt+CH₃OH→Pt—CO+4H⁺+4e⁻  (1)

Pt+H₂O→Pt—OH+H⁺+e⁻  (2)

Pt—CO+Pt—OH→2Pt+CO₂+H⁺+e⁻  (3).

As indicated by the foregoing reactions, the methanol is adsorbed andpartially oxidized by platinum on the surface of the electrode (2).Adsorbed OH, from the hydrolysis of water (3), reacts with the adsorbedCO to produce carbon dioxide and a proton. However, platinum does notadsorb H₂O species well at the potentials fuel cell electrodes operate(e.g., 200 mV-1.5 V). As a result, step (3) is the slowest step in thesequence, limiting the rate of CO removal thereby poisoning thecatalyst. This applies in particular to a Proton exchange membrane fuelcell which is especially sensitive to CO poisoning as a result of itslow operating temperatures.

One technique for alleviating fuel cell performance reduction due toanode CO poisoning is to employ an anode electrocatalyst which is itselfmore poison tolerant, but which still functions as a hydrogen oxidationcatalyst in the presence of carbon monoxide. It is known that thetolerance of platinum poisoning by carbon monoxide is improved byalloying 10 the platinum with ruthenium, preferably compositionscentered around 50:50 atomic ratio (see, e.g., D. Chu and S. Gillman, J.Electrochem. Soc. 1996, 143, 1685).

It has been reported that the success of the platinum-ruthenium catalystalloys is based on the ability of ruthenium to adsorb H₂O species atpotentials where methanol is adsorbing on the platinum and facilitatethe carbon monoxide removal reaction. This dual function, that is, toadsorb both reactants on the catalyst surface on adjacent metal sites,is known as the bifunctional mechanism in accordance with the followingreaction:

Pt—CO +Ru—OH→Pt+Ru+CO₂+H⁺+e⁻  (4).

It has been suggested that having platinum and ruthenium in adjacentsites forms an active site on the catalyst surface where methanol isoxidized in a less poisoning manner because the adjacent metal atoms aremore efficiently adsorbing the methanol and the water reactants.

Although knowledge of phase equilibria and heuristic bondstrength/activity relationships provide some guidance in the search formore effective catalyst compositions, there is at present no way tocalculate the chemical composition of different metals that will affordthe best catalyst activity for the direct methanol-air fuel cellreaction. As such, the search continues for stable, CO poisoningresistant and less costly catalysts having increased electrochemicalactivities.

BRIEF SUMMARY OF THE INVENTION

Among the objects of the invention are the preparation of catalystsbased on platinum, ruthenium and palladium which have a high resistanceto poisoning by carbon monoxide thereby improving the efficiency of afuel cell, decreasing the size of a fuel cell and reducing the cost ofoperating a fuel cell.

Briefly, therefore, the present invention is directed to a ternarycatalyst composition for use in electrochemical reactor devices. Thecatalyst composition consists essentially of, in atomic percentages,platinum from about 20% to about 60%, ruthenium from about 20% to about60%, palladium from about 5% to about 45%, and the ratio of platinum toruthenium is between about 0.6 and about 1.8.

The invention is also directed to a ternary metal alloy composition. Thealloy is characterized by the empirical formula Pt_(x)Ru_(y)Pd_(1-x-y)where x is from about 0.2 to about 0.6, y is from about 0.2 to about0.6, and the difference between y and x is between about −0.2 and 0.2.

Also, the present invention is directed to a fuel cell electrodecomprising a ternary catalyst dispersed on the surface of anelectrically conductive support. The ternary catalyst consistingessentially of, in atomic percentages, platinum from about 20% to about60%, ruthenium from about 20% to about 60%, palladium from about 5% toabout 45%, and the ratio of platinum to ruthenium is between about 0.6and about 1.8.

Further, the present invention is directed to a fuel cell electrodecomprising a ternary catalyst dispersed on the surface of anelectrically conductive support. The ternary catalyst is characterizedby the empirical formula Pt_(x)Ru_(y)Pd_(1-x-y) wherein x is from about0.2 to about 0.6, y is from about 0.2 to about 0.6, and the differencebetween y and x is between about −0.2 and about 0.2.

Additionally, the present invention is directed to a fuel cell a fuelcell comprising an anode, a cathode, a proton exchange membrane betweenthe anode and the cathode, and an electrocatalyst for the catalyticoxidation of a hydrogen-containing fuel. The fuel cell is characterizedin that the electrocatalyst comprises a ternary metal alloy having theempirical formula Pt_(x)Ru_(y)Pd_(1-x-y) wherein x is from about 0.2 toabout 0.6, y is from about 0.2 to about 0.6, and the ratio of x to y isbetween about 0.6 and about 1.8.

In yet another aspect, the present invention is directed to a method forthe electrochemical conversion of a hydrocarbon-based fuel and oxygen towater, carbon dioxide and electricity in a fuel cell comprising ananode, a cathode, a proton exchange membrane electrolyte therebetween,and an electrically conductive external circuit connecting the anode andcathode. The method comprising contacting the hydrocarbon-based fuelwith a ternary metal alloy catalyst to catalytically oxidize the fuel,the ternary catalyst consisting essentially of, in atomic percentages,platinum from about 20% to about 60%, ruthenium from about 20% to about60%, and palladium from about 5% to about 45%, with the difference inthe atomic percentages of ruthenium and platinum being no greater thanabout 20 atomic percent.

The foregoing and other features and advantages of the present inventionwill become more apparent from the following description andaccompanying drawing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic structural view showing essential members of amethanol fuel cell.

FIG. 2 is a side view of a methanol fuel cell.

FIG. 3 is a graph comparing the catalytic activity, at a constantvoltage and as a function of time, of several alloy compositionsincluding PtPd binary alloys, a PtPd binary alloy, and PtRuPd ternaryalloys. Only the PtRuPd alloy compositions on Electrodes #4-#12 arewithin the scope of the claimed invention.

FIG. 4 is a graph comparing the catalytic activity of a PtRuPd ternaryalloy composition to a PtRu binary composition as a function of voltage.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a multi-component noble metal alloycomposition having improved catalytic activity over platinum-rutheniumbinary alloys in fuel cells. In particular, the present invention isdirected to certain PtRuPd ternary alloy compositions containing, inatomic percentages, about 20% to about 60% platinum, about 20% to about60% ruthenium and about 5% to about 45% palladium. Surprisingly, whenthe relative concentration of platinum to ruthenium is controlled withina prescribed range, the ternary alloy possesses significantly improvedcatalytic activity over platinum-ruthenium binary alloys and evenpreviously reported platinum-ruthenium-palladium ternary alloys. Ingeneral, the concentrations of platinum and ruthenium are controlled toprovide (i) a ternary alloy having an atomic ratio of platinum toruthenium of about 0.6 to about 1.8, preferably about 0.7 to about 1.2and still more preferably about 0.7 to about 1.0 or, alternatively, (ii)a ternary alloy in which the difference between the atomic percentagesof platinum and ruthenium is no more than about 20 atomic percent,preferably 15 atomic percent and still more preferably 10 atomicpercent.

In one embodiment of the present invention, therefore, the PtRuPdternary alloy contains, in atomic percentages, about 25% to about 50%platinum and about 25% to about 55% ruthenium wherein (i) the atomicratio of platinum to ruthenium is about 0.6 to about 1.8, preferablyabout 0.7 to about 1.2 and still more preferably about 0.7 to about 1.0or, alternatively, (ii) the difference between the atomic percentages ofplatinum and ruthenium is no more than about 20 atomic percent,preferably 15 atomic percent and still more preferably 10 atomicpercent. In another embodiment of the present invention, the PtRuPdternary alloy contains, in atomic percentages, about 30% to about 45%platinum and about 35% to about 50% ruthenium wherein (i) the atomicratio of platinum to ruthenium is preferably about 0.7 to about 1.2 andstill more preferably about 0.7 to about 1.0 or, alternatively, (ii) thedifference between the atomic percentages of platinum and ruthenium ispreferably no more than about 15 atomic percent, more preferably no morethan about 10 atomic percent. In a further embodiment of the presentinvention, the PtRuPd ternary alloy contains, in atomic percentages,about 30% to about 40% platinum and about 35% to about 45% rutheniumwherein (i) the atomic ratio of platinum to ruthenium is preferablyabout 0.7 to about 1.2 and still more preferably about 0.7 to about 1.0or, alternatively, (ii) the difference between the atomic percentages ofplatinum and ruthenium is preferably no more than about 15 atomicpercent, more preferably no more than about 10 atomic percent. In afurther embodiment of the present invention, the PtRuPd ternary alloycontains, in atomic percentages, about 25% to about 45% platinum andabout 40% ruthenium and about 15% to about 35% palladium. Specificalloys which have been found to exhibit a relatively high methanoloxidation activity include the alloys corresponding the empiricalformula Pt_(x)Ru_(y)Pd_(1-x-y) wherein x and y have the followingvalues.

X Y 30 40 35 40 40 35 40 50 42 25 40 40 35 35 40 45 25 40 40 55 45 50 3545 45 45 45 40 50 45 25 35 30 35 35 50 30 45 35 55

Although the PtRuPd ternary alloy compositions of the present inventioncan be used in a phosphoric acid fuel cell, they are particularly usefulin a direct methanol fuel cell. As shown in FIG. 1 and FIG. 2, a directmethanol fuel cell has a methanol electrode (fuel electrode or anode) 2and an air electrode (oxidizer electrode or cathode) 3. In between theelectrodes, a proton exchange membrane 3 serves as an electrolyte.

Preferably, in a fuel cell according to the present invention, theproton exchange membrane 1, the anode 2 and the cathode 3 are integratedinto one body, and thus there is no contact resistance between theelectrodes 2 and 3 and the proton exchange membrane 1. Currentcollectors 4 and 5 are at the anode and cathode, respectively. Amethanol fuel chamber is indicated by numeral 8 and an air chamber isindicated by numeral 9. Numeral 6 is a sealant for the methanol fuelchamber and numeral 7 is a sealant for the air chamber. It is desirableto use a strongly acidic ion exchange membrane (e.g., perfluorosulphonicacid based membranes are widely used).

In general, electricity is generated by methanol combustion (i.e.,methanol and oxygen react to form water, carbon dioxide andelectricity). This is accomplished in the above-described fuel cell byintroducing the methanol into the methanol fuel chamber 8, while oxygen,preferably air is introduced into the air chamber 9, whereby an electriccurrent can be immediately withdrawn therefrom into an outer circuit.Ideally, the methanol is oxidized at the anode to produce carbon dioxidegas, hydrogen ions and electrons. The thus formed hydrogen ions migratethrough the strongly acidic proton exchange membrane 1 and react withoxygen and electrons from the outer circuit at the cathode 3 to formwater. Typically, the methanol is introduced as a dilute acidic solutionto enhance the chemical reaction thereby increasing power output (e.g.,a 0.1 M methanol/0.5 M sulfuric acid solution).

Typically, the proton exchange membranes must remain hydrated duringoperation of the fuel cell in order to prevent loss of ionic conduction,thus the membrane is preferably heat-resistant up to about 100-1200° C.Proton exchange membranes usually have reduction and oxidationstability, resistance to acid and hydrolysis, sufficiently lowelectrical resistivity (e.g., <10 Ω·cm), and low hydrogen or oxygenpermeation. Additionally, proton exchange membranes are usuallyhydrophilic, this ensures proton conduction (by reversed diffusion ofwater to the anode), and prevents the membrane from drying out therebyreducing the electrical conductivity. For the sake of convenience, thelayer thickness of the membranes is typically between 50 and 200 μm. Ingeneral, the foregoing properties are achieved with materials which haveno aliphatic hydrogen-carbon bonds, which, for example, is achieved byreplacing hydrogen with fluorine or by the presence of aromaticstructures; the proton conduction results from the incorporation ofsulfonic acid groups (high acid strength). Suitable proton-conductingmembranes also include perfluorinated sulfonated polymers such asNafion® and its derivatives produced by E.I. du Pont de Nemours & Co.,Wilmington, Del. Nafion® is based on a copolymer made fromtetrafluoroethylene and perfluorovinylether, and is provided withsulfonic groups working as ion-exchanging groups. Other suitable protonexchange membranes are produced with monomers such as perfluorinatedcompounds (e.g., octafluorocyclobutane and perfluorobenzene), or evenmonomers with C—H bonds which, in a plasma polymer, do not form anyaliphatic H atoms which could constitute attack sites for oxidativebreakdown.

In general, the electrodes of the present invention comprise anelectrically conductive material and are in contact with the PdRuPtternary catalyst of the present invention. The electrically conductivesupport is typically inorganic, preferably a carbon support. The carbonsupports may be predominantly amorphous or graphitic. They may beprepared commercially, or specifically treated to increase theirgraphitic nature (e.g., heat treated at a high temperature in vacuum orin an inert gas atmosphere) thereby increasing corrosion resistance. Forexample, it may be oil furnace black, acetylene black, graphite paper,carbon fabric or carbon aerogel. Preferably, the electrode is designedto increase cell efficiency by enhancing contact between the reactant(i.e., fuel or oxygen), the electrolyte and the electrocatalyst. Inparticular, porous or gas diffusion electrodes are typically used sincethey allow the fuel/oxidizer to enter the electrode from the face of theelectrode exposed to the reactant gas stream (back face), and theelectrolyte to penetrate through the face of the electrode exposed tothe electrolyte (front face), and products, particularly water todiffuse out of the electrode. Preferably, carbon black supports have aBrunauer, Emmett and Teller (BET) surface area of between 0 and 2000m²/g, and preferably between 30 and 400 m²/g, more preferably between 60to 250 m²/g. On the other hand, the carbon aerogel preferably has anelectrical conductivity of between 10⁻² and 10³ Ω⁻¹·cm⁻¹ and a densityof between 0.06 and 0.7 g/cm³; the pore size is between 20 and 100 nm(porosity up to about 95%).

Preferably, the proton exchange membrane, electrodes and catalystmaterials are in contact. This is generally accomplished by depositingthe catalyst either on the electrode, or the proton exchange membrane,and then the electrode and membrane placed in contact. The alloycatalysts of this invention can be deposited on either substrate by avariety of methods, including, plasma deposition, powder application,chemical plating, and sputtering. Plasma deposition generally entailsdepositing a thin layer (e.g., between 3 and 50 μm, preferably between 5and 20 μm) of a catalyst composition on the membrane using low-pressureplasma. By way of example, an organic platinum compound such astrimethylcyclopentadienylplatinum is gaseous between 10⁴ and 10 mbar andcan be excited using radio-frequency, microwaves or an electroncyclotron resonance transmitter to deposit platinum on the membrane.According to another procedure, catalyst powder is distributed onto theproton exchange membrane surface and integrated at an elevatedtemperature under pressure. If, however, the amount of catalystparticles exceeds about 2 mg/cm² the inclusion of a binder such aspolytetrafluoroethylene is common. Further, the catalyst may be platedwith dispersed relatively small particles, e.g., about 20-200 Å, morepreferably about 20-100 Å. This increases the catalyst surface areawhich in turn increases the number of reaction sites leading to improvedcell efficiency. In one such chemical plating process, for example, apowdery carrier material such as conductive carbon black is contactedwith an aqueous solution or aqueous suspension (slurry) of compounds ofmetallic components constituting the alloy to permit adsorption orimpregnation of the metallic compounds or their ions on or in thecarrier. Then, while the slurry is stirred at high speed, a dilutesolution of suitable fixing agent such as ammonia, hydrazine, formicacid or formalin is slowly added dropwise to disperse and deposit themetallic components on the carrier as insoluble compounds or partlyreduced fine metal particles.

The surface concentration of catalyst on the membrane or electrode isbased in part on the desired power output and cost for a particular fuelcell. In general, power output increases with increasing concentration,however, there is a level beyond which performance is not improved.Likewise, the cost of a fuel cell increases with increasingconcentration. Thus, the surface concentration of catalyst is selectedto meet the application requirements. For example, a fuel cell designedto meet the requirements of a demanding application such as an outerspace vehicle will usually have a surface concentration of catalystsufficient to maximize the fuel cell power output. Preferably, thedesired power output is obtained with as little catalyst as possible.Typically, it is desirable that about 0.25 to about 6 mg/cm² of catalystparticles be in contact with the electrodes. If the surfaceconcentration of catalyst particles is less than about 0.25 mg/cm², thecell performance usually declines, whereas, above about 6 mg/cm² thecell performance is usually not improved.

To promote contact between the collector, electrode, catalyst andmembrane, the layers are usually compressed at high temperature. Thehousings of the individual fuel cells are configured in such a way thata good gas supply is ensured, and at the same time the product water canbe discharged properly. Typically, several fuel cells are joined to formstacks, so that the total power output is increased to economicallyfeasible levels.

In general, the ternary catalyst and electrodes of the present inventionmay be used to catalyze any fuel containing hydrogen (e.g., hydrogen andreformated-hydrogen fuels). The improved catalytic activity of thePtRuPd ternary alloys, however, are particularly realized in thecatalysis of hydrocarbon-based fuels. Applicable hydrocarbon-based fuelsinclude saturated hydrocarbons such as methane (natural gas), ethane,propane and butane; garbage off-gas; oxygenated hydrocarbons such asmethanol and ethanol; and fossil fuels such as gasoline and kerosene;and mixtures thereof. The most preferred fuel, however, is methanol.

To achieve the full ion-conducting property of proton exchangemembranes, suitable acids (gases or liquids) are typically added to thefuel. For example, SO₂, SO₃, sulfuric acid, trifluoromethanesulfonicacid or the fluoride thereof, also strongly acidic carboxylic acids suchas trifluoroacetic acid, and volatile phosphoric acid compounds may beused (see, e.g., “Ber. Bunsenges. Phys. Chem.”, Volume 98 (1994), pages631 to 635).

Definitions

Activity is defined as the maximum sustainable, or steady state, current(Amps) obtained from the catalyst, when fabricated into an electrode, ata given electric potential, or efficiency (Volts). Additionally, becauseof differences in the geometric area of electrodes, when comparingdifferent catalysts, activity is often expressed in terms of currentdensity (A/cm²).

EXAMPLE 1

A tremendous amount of research has concentrated on exploring theactivity of surface modified binary, and to a much lesser extentternary, alloys of platinum in an attempt to both increase theefficiency of and reduce the amount of precious metals in the anode partof the fuel cell. Although electrodeposition was explored as a route tothe synthesis of anode materials (see, e.g., F. Richarz et al. SurfaceScience, 1995, 335, 361), only a few compositions were actuallyprepared, and these compositions were made using traditional singlepoint electrodeposition techniques.

In contrast, the catalyst alloy compositions of this invention wereprepared using the combinatorial techniques disclosed in U.S. patentapplication Ser. No. 09/119,187, filed Jul. 20, 1998. Specifically, anarray of independent electrodes (with areas of between about 1 and 2mm²) were fabricated on inert substrates (e.g., glass, quartz, sapphirealumina, plastics, and thermally treated silicon). The individualelectrodes were located substantially in the center of the substrate,and were connected to contact pads around the periphery of the substratewith wires. The electrodes, associated wires, and contact pads werefabricated from conducting materials (e.g., gold, silver, platinum,copper or other commonly used electrode materials). In a preferredembodiment, the arrays were fabricated on standard 3″ (about 7.5 cm)thermally oxidized single crystal silicon wafers, and the electrodeswere gold with surface areas of about 1.26 mm².

A patterned insulating layer covered the wires and an inner portion ofthe peripheral contact pads, but left the electrodes and the outerportion of the peripheral contact pads exposed (preferably approximatelyhalf of the contact pad is covered with this insulating layer). Becauseof the insulating layer, it is possible to connect a lead (e.g., analligator clip) to the outer portion of a given contact pad and addressits associated electrode while the array is immersed in solution,without having to worry about reactions that can occur on the wires orperipheral contact pads. The insulating layer may be, for example,glass, silica, alumina, magnesium oxide, silicon nitride, boron nitride,yttrium oxide, titanium dioxide, hardened photoresist, or other suitablematerial known to be insulating in nature.

Once a suitable inert substrate was provided, in this case thermallyoxidized single crystal silicon was selected, photolithographictechniques were used to design and fabricate electrode patterns on it.By applying a predetermined amount of photoresist to the substrate,photolyzing preselected regions of the photoresist, removing thoseregions that have been photolyzed (e.g., by using an appropriatedeveloper), depositing one or more metals over the entire surface andremoving predetermined regions of these metals (e.g. by dissolving theunderlying photoresist), intricate patterns of individually addressableelectrodes were fabricated on the substrate.

The fabricated arrays consisted of a plurality of individuallyaddressable electrodes that were insulated from each other (by adequatespacing) and from the substrate (fabricated on an insulating substrate),and whose interconnects were insulated from the electrochemical testingsolution (by the hardened photoresist or other suitable insulatingmaterial).

Materials were deposited on the above described electrode arrays toprepare a library of compositions by the electrodeposition of speciesfrom solution using standard electrochemical methods. More specifically,the depositions were carried out by immersing the electrode array in astandard electrochemical deposition chamber containing the array, aplatinum mesh counter electrode, and a reference electrode (e.g.,Ag/AgCl). The chamber was filled with a plating solution containingknown amounts of source material to be deposited. By selecting a givenelectrode and applying a predetermined potential for a predeterminedamount of time, a particular composition of materials (which may or maynot correspond to the exact composition of the plating solution) wasdeposited on the electrode surface. Variations in the compositionsdeposited may be obtained either by directly changing the solutioncomposition for each deposition or by using different electrochemicaldeposition techniques, or both. Examples of how one may change theelectrode composition by changing the deposition technique can include:changing the deposition potential, changing the length of the depositiontime, varying the counter anions, using different concentrations of eachspecies, and even using different electrochemical deposition programs(e.g., potentiostatic oxidation/reduction, galvanostaticoxidation/reduction, potential square-wave voltammetry, potentialstair-step voltammetry, etc.). In any event, through repeated depositionsteps, a variety of materials were deposited on the array.

After synthesizing the various alloy compositions on the array, thedifferent alloys were screened for methanol oxidation to determinerelative catalytic activity against a standard alloy composition.

EXAMPLE 2

Using the procedures described in Example 1 to synthesize catalystcompositions by electrodeposition, the following aqueous stock solutionswere prepared in 0.5 M sulfuric acid (H₂SO₄): 0.03 M platinum chloride(H₂PtCl₆), 0.05 M ruthenium chloride (RuCl₃), and 0.03 M palladiumchloride (PdCl₃). The sulfuric acid merely served as an electrolytethereby increasing the plating efficiency. A standard plating solutionwas created by combining 15 ml of the platinum chloride stock solutionand 12 ml of the ruthenium chloride stock solution. The electrodes onthe array were then immersed in the standard plating solution. Apotential of −0.93 V vs Ag/AgCl was applied for 2 minutes to the firstelectrode (Electrode #1 in FIG. 3). The thickness of the layer depositedon the electrode ranged from about 1500 and about 2000 Å. Thecomposition of the PtRu alloy plated under these conditions isrepresented by the formula Pt_(0.65)Ru_(0.35).

To synthesize a PtRuPd ternary alloy composition, an aliquot of thepalladium chloride stock solution (e.g., 1 ml) was added to the standardPtRu plating solution and the second electrode was then plated at −0.93V vs. Ag/AgCl for 2 minutes. The amount of palladium in subsequentlydeposited alloys was increased by adding palladium chloride stocksolution to the plating solution. Thus, a library of alloy compositionscan be created by varying the relative amounts of different stocksolutions in the plating solution (e.g., Electrodes #3-#13 in FIG. 3were plated under identical conditions except that the relative amountsof the stock solutions were varied). Also, PdRu binary alloys weresynthesized (e.g., Electrode #13 which corresponds to the formulaPd_(0.50)Ru_(0.50))

After synthesizing the various alloy compositions on the array, thedifferent compositions were screened for methanol oxidation activity byplacing the array into an electrochemical cell, which was filled with aroom temperature solution of 1M methanol in 0.5 M H₂SO₄. The cell alsocontained in Hg/HgSO₄ reference electrode and a platinum mesh counterelectrode. Chronoamperometry measurements (i.e., holding a givenelectrode at a given potential and measuring the current that passes asa function of time) were then performed on all of the electrodes bypulsing each individual electrode to a potential of 0.3 V vs NHE (NormalHydrogen Electrode) and holding it there for about 6 minutes whilemonitoring and recording the current that flowed. Of particular interestwere alloy compositions which showed improved catalytic activity ascompared to PtRu binary alloys in general, and preferably PtRu alloyscentered around a 50:50 atomic ratio (e.g., Pt_(0.45)Ru_(0.55) andPt_(0.55)Ru_(0.45))

Several electroplated alloys were analyzed using x-ray fluorescence(XRF) to determine their compositions. It is commonly accepted thatchemical compositions determined using x-ray fluorescence are withinabout 5% of the actual composition. A comparison of relative oxidationcurrent (normalized to the most active catalyst, the alloy on Electrode#9) for several of the alloy compositions in the library is provided inTable 1.

TABLE 1 Pt in Ru in Pd in Relative alloy alloy alloy Oxidation Electrode(atomic %) (atomic %) (atomic %) Current # 30 40 30 1   9 35 40 25 0.858 40 35 25 0.6  7 40 50 10 0.59 42 25 33 0.55 10  40 40 20 0.54 6 35 3530 0.50 40 45 15 0.48 11  45 55  0 0.45 25 40 35  0.436 40 55  5 0.43 4550  5 0.43 35 45 20 0.40 12  45 45 10 0.40 45 40 15 0.38 5 50 45  5 0.374 25 35 40 0.37 30 35 35 0.36 35 50 15 0.36 30 45 25 0.33 35 55 10 0.3255 45  0 0.30 25 45 30 0.26 30 30 40 0.26 25 50 25 0.24 65 35  0 0.2  150 50  0 0.18 2 60 40  0 0.18 30 50 20 0.15 40 60  0 0.15 35 60  5 0.1 3 20 35 45 0.09 20 40 40 0.07  0 50 50 0.0  13 

Specific ternary alloys listed in the above table which have aparticularly high relative methanol oxidation activity include: platinumat about 30%, ruthenium at about 40%, and palladium at about 30%platinum, the most preferred embodiment; platinum at about 35%,ruthenium at about 40%, and palladium at about 25%; platinum at about40%, ruthenium at about 35%, and palladium at about 25%; platinum atabout 40%, ruthenium at about 50%, and palladium at about 10%; platinumat about platinum at about 42%, ruthenium at about 25%, and palladium atabout 33%; platinum at about 40%, ruthenium at about 40% and palladiumat about 20%; and platinum at about 35%, ruthenium at about 35% andpalladium at about 30%.

As indicated in FIG. 3, several alloy compositions showed increasedcatalytic activity over the Pt_(0.65)Ru_(0.35) alloy. Specifically, thedata represented in FIG. 3 indicates that the alloy compositionsdeposited on Electrodes #4-#12 show increased methanol oxidationactivity compared to the Pt_(0.65)Ru_(0.35) alloy. Additionally, it isevident that the Pd_(0.50)Ru_(0.50) alloy deposited on Electrode #13 hasa decreased methanol oxidation activity compared to the standard PtRualloy and the PtRuPd ternary alloys of the present invention.

Two of the foregoing electroplated alloys were subjected to powdersynthesizing to gain information relevant to producing a fuel cell withdispersed catalyst compositions of the present invention. First, theplating solutions deposited on Electrodes #9 and #10 were plated on alarger area electrode (about 1 cm²) and the plated alloy wasmechanically removed and its x-ray fluorescence (XRF) spectrum wasmeasured. Then the alloys were synthesized in powder form using aco-precipitation technique which entails slow dropwise additions of a0.2 M NaBH₄ solution into a solution containing H₂PtCl₆, RuCl₃, PdCl₃.The slurry was maintained at about 80° C. for about 3 hours, filtered,vigorously washed with distilled water, and dried for about 4 hours atabout 110° C. X-ray fluorescence was applied to the synthesized powderand the resultant spectrum was compared with that of the desiredelectroplated alloy. When the XRF spectra are identical, the compositionof the powder and electroplate alloys are identical. Typically, severaliterations of alloy precipitation are necessary to produce a powderalloy composition which corresponds to the electroplated alloy. For theElectrode #9 alloy, a precipitation solution containing 10 ml of 0.03 MH₂PtCl₆, 4 ml of 0.05 M RuCl₃, and 9 ml of 0.03 M PdCl₃ yielded a powderalloy catalyst of identical composition. The alloy powder was then beanalyzed with more precise techniques to confirm its composition.Rutherford backscattering spectroscopy determined that the chemicalcomposition of the precipitated powder alloys corresponding toElectrodes #9 and #10 were Pt_(0.3)Ru_(0.4)Pd_(0.3) andPt_(0.42)Ru_(0.25)Pd_(0.33), respectively. It is commonly accepted thatthe chemical compositions determined using the Rutherford backscatteringmethod are within about 2% of the actual composition.

The activity of the most preferred ternary alloy,Pt_(0.3)Ru_(0.4)Pd_(0.3), was also compared to that of Pt₆₅Ru₃₅ as afunction of increasing voltage (see, FIG. 4). FIG. 4 indicates that thePt_(0.3)Ru_(0.4)Pd_(0.3) alloy oxidizes methanol at lower electricalpotentials than the PtRu standard. Also, the Pt_(0.3)Ru_(0.4)Pd_(0.3)alloy has a greater catalytic activity for a given potential than thestandard. Further, the difference in catalytic activity between thePt_(0.3)Ru_(0.4)Pd_(0.3) alloy and the standard increases withincreasing voltage.

It is to be understood that the above description is intended to beillustrative and not restrictive. Many embodiments will be apparent tothose of skill in the art upon reading the above description. The scopeof the invention should therefore be determined not with reference tothe above description alone, but should also be determined withreference to the claims and the full scope of equivalents to which suchclaims are entitled. The disclosures of all articles, patents andreferences, including patent applications and publications, areincorporated herein by reference for all purposes.

What is claimed is:
 1. A ternary catalyst composition for use inelectrochemical reactor devices consisting essentially of, in atomicpercentages, platinum from about 20% to about 60%, ruthenium from about20% to about 60%, and palladium from about 5% to about 45%, with theatomic ratio of platinum to ruthenium being between about 0.7 and about1.2.
 2. The catalyst composition of claim 1 wherein the concentration ofplatinum is from about 25% to about 50%, and the concentration ofruthenium is from about 25% to about 55%.
 3. The catalyst of claim 1wherein the atomic ratio of platinum to ruthenium is between about 0.7and about 1.0.
 4. The catalyst composition of claim 1 wherein theconcentration of platinum is from about 30% to about 45%, and theconcentration of ruthenium is from about 35% to about 50%.
 5. Thecatalyst of claim 4 wherein the atomic ratio of platinum to ruthenium isbetween about 0.7 and about 1.0.
 6. The catalyst composition of claim 1wherein the concentration of platinum is from about 30% to about 40%,and the concentration of ruthenium is from about 35% to about 45%. 7.The catalyst of claim 6 wherein the atomic ratio of platinum toruthenium is between about 0.7 and about 1.0.
 8. The catalystcomposition of claim 1 wherein the concentration of platinum is fromabout 25% to about 45%, the concentration of ruthenium is about 40%, andthe concentration of palladium is from about 15% to about 35%.
 9. Thecatalyst composition of claim 1 wherein the concentration of platinum isabout 30%, the concentration of ruthenium is about 40%, and theconcentration of palladium is about 30%.
 10. The catalyst composition ofclaim 1 wherein the concentration of platinum is about 35%, theconcentration of ruthenium is about 40%, and the concentration ofpalladium is about 25%.
 11. The catalyst composition of claim 1 whereinthe concentration of platinum is about 42%, the concentration ofruthenium is about 25%, and the concentration of palladium is about 33%.12. A ternary metal alloy composition characterized by the empiricalformula Pt_(x)Ru_(y)Pd_(1-x-y) wherein x is from about 0.25 to about0.5, y is from about 0.25 to about 0.55, and the difference between yand x is between about −0.2 and about 0.2.
 13. The ternary metal alloycomposition of claim 12 wherein the difference between y and x isbetween about −0.15 and about 0.15.
 14. The ternary metal alloycomposition of claim 12 wherein the difference between y and x isbetween about −0.10 and about 0.10.
 15. The ternary metal alloycomposition of claim 12 wherein x is from about 0.3 to about 0.45, and yis from about 0.35 to about 0.5.
 16. The ternary metal alloy compositionof claim 12 wherein the difference between y and x is between about−0.15 and about 0.15.
 17. The ternary metal alloy composition of claim12 wherein the difference between y and x is between about −0.10 andabout 0.10.
 18. The ternary metal alloy composition of claim 1 wherein xis from about 0.3 to about 0.4, and y is from about 0.35 to about 0.45.19. The ternary metal alloy composition of claim 18 wherein thedifference between y and x is between about −0.15 and about 0.15. 20.The ternary metal alloy composition of claim 18 wherein the differencebetween y and x is between about −0.10 and about 0.10.
 21. The ternarymetal alloy composition of claim 12 wherein x is 0.3, and y is about0.4.
 22. The ternary metal alloy composition of claim 12 wherein x is0.35, and y is about 0.4.
 23. The ternary metal alloy composition ofclaim 12 wherein x is 0.4, and y is about 0.4.
 24. The ternary metalalloy composition of claim 12 wherein x is 0.42, and y is about 0.25.25. A fuel cell electrode, the electrode comprising a ternary catalystdispersed on the surface of an electrically conductive support, theternary catalyst consisting essentially of, in atomic percentages,platinum from about 20% to about 60%, ruthenium from about 20% to about60%, and palladium from about 5% to about 45%, with the atomic ratio ofplatinum to ruthenium being between about 0.7 and about 1.2.
 26. A fuelcell electrode, the electrode comprising a ternary catalyst dispersed onthe surface of an electrically conductive support, the ternary catalystcharacterized by the empirical formula Pt_(x)Ru_(y)Pd_(1-x-y) wherein xis from about 0.25 to about 0.5, y is from about 0.25 to about 0.55, andthe difference between y and x is between about -0.2 and about 0.2. 27.A fuel cell comprising an anode, a cathode, a proton exchange membranebetween the anode and the cathode, and an electrocatalyst for thecatalytic oxidation of a hydrogen-containing fuel, the fuel cellcharacterized in that the electrocatalyst comprises a ternary metalalloy having the empirical formula Pt_(x)Ru_(y)Pd_(1-x-y) wherein x isfrom about 0.2 to about 0.6, y is from about 0.2 to about 0.6, and theratio of x to y is between about 0.7 and about 1.2.
 28. The fuel cell ofclaim 27 wherein x is from about 0.3 to about 0.45, and y is from about0.35 to about 0.5.
 29. The fuel cell of claim 27 wherein x is from about0.3 to about 0.4, and y is from about 0.35 to about 0.45.
 30. The fuelcell of claim 27 wherein x is 0.3, and y is about 0.4.
 31. The fuel cellof claim 27 wherein x is 0.35, and y is about 0.4.
 32. The fuel cell ofclaim 27 wherein x is 0.4, and y is about 0.4.
 33. The fuel cell ofclaim 27 wherein x is 0.42, and y is about 0.25.
 34. The fuel cell ofclaim 27 wherein the fuel is a hydrocarbon-based fuel.
 35. The fuel cellof claim 34 wherein the fuel comprises methanol.
 36. The fuel cell ofclaim 34 wherein the electrocatalyst is on the surface of the protonexchange membrane and in contact with the anode.
 37. The fuel cell ofclaim 34 wherein the electrocatalyst is on the surface of the anode andin contact with the proton exchange membrane.